The basic rocks is included in the trondhjemitic migmatite or in the tonalitic migmatite, at the midstream of the river Horoman, Hidaka province.
In this paper, some microscopical relations between the component minerals of the migmatite and of the basic xenolith are described.
The auther concludes that the basic xenolith is the origin from the biotite rich hornfelsic rock which is basified before the xenolith is included in the migmatite.

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Tazawa district here mentioned is situated at the central part of the Dewa Mountains between the Shonai and Mogami oil fields, Yamagata Prefecture. According to the present writer's study from 1950 to 1955 the district is chracterized by the frequent volcanic activitis which occured in the Neogene and are represented by flows, pyroclastics, dykes and sills.
The Neogene Tertiary of the district is divided into the Tazawa, Tate yama, Kusanagi and Kitamata formations from lower to upper.
The sequence of the volcanic activities in the district is traced as follows.
1st. stage. Submarine eruption and explosion of tholeiitic basalt(SiO₂=47, 28%-52, 48%) in the Tazawa formation. A part of the basalt changes to spilitic character (NaO₂=3, 63%) by albitization. The great amount of this basaltic reeks was followed by the formation of geosynclinal character.
2nd. stage. Center eruption of Taizosan andesite, which is augite andesite (SiO₂=53, 72%), two pyroxene andesite (SiO₂=56, 12%) and hornblende andesite (SiO₂=58, 68%). This rocks has petrographical chracter which is very coarse grain and rich in plagioclase phenocryst. However, at last stage of this activity, it is very fine grain type.
3rd. stage. Intrusion of olivin basalt (SiO₂=47, 28%) represented by dykes and sills. Parallel dyke swarm of basalt is restricted in the Tazawa and Tateyama formatins and sills occur only in the Kusanagi formation. At the later stage the rocks changes to doleritic chracter.
4th, stage. Subordinate acidic tuff explosion is broadly traced in this area. This tuff is liparitic pumice, and thinly bedded in the boundary of the Kusanagi and Kitamata formations.

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An orbicular diorite was discovered from Kawaguchi, Akka Village, Iwate Prefecture. This is the first occurrence of orbicular rock from Kitakami Mountainland. The host rock is biotite-hornblende-quartz-diorite, which belongs to the Kawaguchi type of the Tanohata granite. The orbicular rock consists of orbicules and schistose matrix, the latter has similar petrographical properties to the former and gradually merges to the host rock. Most of the orbicules show ovoidal form elongated parallel to the schistosity of the matrix, the boundary between the orbicules and the matrix being sharp. The orbicules consist of plagioclase, green hornblende, brown biotite, and small amounts of quartz and potash feldspar as essential minerals, of magnetite as accessory minerals. Several types of orbicules are observed, though their petrographical features are not so different from each other.
The most typical orbicule consists of four concentric parts, namely nucleus, inner zone, radial zone, and outer zone. The nucleus is mediumgrained and dioritic, the inner zone being fine grained and dioritic. The radial zone is characterized by the radial arrangement of plagioclase, while in the outer zone plagioclase and mafic minerals are arranged tangentially. Two kinds of plagioclase are noted. The coarse-grained crystal is so-called mantleblast with calcic core (bytownite-anorthite) and sodic rim (oligoclase-andesine). The fine-grained crystal is granular and occurs often as mosaic aggregates. Twinning after albite-Carlsbad and Carlsbad law is common. In the radial zone, polysynthetic twins after albite or pericline law are combined with Carlsbad twins, showing very complex and interesting feature twinning. It is assumed that the orbicular rock under question is derived from some gabbroic rock by some migmatitic action under the addition of granitic matter, and its concentric structure is formed during the process of metasomatism probably by so-called metamorphic differentiation. At later stage the orbicular rock and the host was deformed under stress condition due to the flow movement of the mass.

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Besides a typical hexagonal pattern, several weak diffraction lines are discernible in the X-ray powder photograph of a synthesized indialite. It seems that the weak lines are caused from the presence of super-lattice or crystal-distortion in the indialite lattice, and therefore, the crystal is not necessarily hexagonal in the strict sense of the word. Thus the optically biaxial character of the indialite corresponds with the appearance of the weak diffraction lines.

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